The present invention relates to a new glass composition characterized by fast ionic transport contemplated for use as a solid electrolyte in various cells. The invention is contemplated for use in power cells, secondary cells and the like.
Unitl recently good ionic conductors were selected almost exclusively from crystalline solid electrolytes. For example, sodium-sulfur electrochemical cells often employ beta alumina as an electrolyte for sodium ion transport. In 1976, a class of crystalline materials was discovered having a sodium conduction comparable to the beta aluminas. These materials were called NASICONS, an acronym for sodium superionic conductors and had a reported stoichiometry of Na.sub.1+x Zr.sub.2 Si.sub.x P.sub.3-x O.sub.12. Where x is likely to be 2, the "ideal" NASICON material would be Na.sub.3 Zr.sub.2 Si.sub.2 PO.sub.12. When the inventors attempted to make this "ideal" NASICON material using normal techniques for producing crystalline three dimensional compounds, the material could not be made. Also, during 1979 several other groups reported unsuccessful attempts to make the above set forth NASICON material even using exotic techniques.
Continued work by the inventors with the "ideal" NASICON formula indicated an over abundance of zirconium oxide and with this in mind a new formula was discovered: EQU Na.sub.1+x Zr.sub.2-x/3 Si.sub.x P.sub.3-x O.sub.12-2x/3.
Nevertheless, even at this time the NASICON materials were still thought to be three dimensional crystalline compounds. The basis of this invention was the discovery that the above set forth formula, could be rewritten as a traditional glass formula, and for X=3 is as follows:
(Na.sub.2 O).sub.2 (ZrO.sub.2)(SiO.sub.2).sub.3 wherein the sodium oxide acted as a network modifier, the zirconium oxide acted as intermediate and the silicon dioxide acted as the network former. Even after the recognition that the NASICON crystalline formula could be rewritten as a glass, it was yet to be determined whether the stoichiometry could be prepared in the form of a glass and whether the glass, if formed, would demonstrate super ionic conduction and whether the glass formulation could prove resistant to the corrosive effects of molten sodium, molten sulfur and the other materials found in typical batteries at the operating temperatures thereof.